Uses for Fish Tank Water from Water Changes

Any aquarist completes the regular, sometimes tedious, task of changing their fish tank water. Some aim for 10% changes, others 50%, maybe every week to as little as monthly – if they do water changes at all. This is all dependent upon tank setup, gear and plants, as well as the time they invest into their hobby. Regardless of the particulars, there is generally an excess of wastewater which is usually, immediately, disposed of. One of our favorite things to do is find ways to reuse and repurpose, so let’s take a look at this today. (Our weekly video covers this topic, which can be seen here).

Some fish produce more waste, this is a well known fact. A betta, compared to a fancy goldfish, would create far less of a bio load by comparison, simply due to their physiology differences (i.e.: stomach vs no stomach), as well as natural environmental specifics (i.e.: cold water vs tropical). Water change frequency is dependent upon need, stocking, tank parameters, amount of plants, etc. Whenever you remove wastewater, you are also removing some good water, too – people use this as a reason to execute larger, yet fewer, changes. On any given afternoon, you may find yourself with several gallons of tank water, depending on your aquariums and capacities, and your first instinct may be to cart it outside and dump it on the lawn (without giving a second thought to the by-product you just disposed of). But, how could you put it to use, instead?

First, let’s consider what’s in wastewater. Most obviously, it contains fish/invertebrate/amphibian waste (both solid and liquid), as well as uneaten and spoiling food, rotting plant limbs and leaves, and possibly decaying pieces of fish such as scales, fins, and more (even the best hobbyist loses fish from time to time). In a well balanced tank, most of these waste products would be broken down by nitrifying bacteria, and used as food for live plants. But, did you also know, your tank water contains trace nutrients? These components are what support a planted tank, and cause them to thrive, and also makes aquaponic and hydroponic setups possible! So, it’s easy to conclude that this valuable resource should be put to use growing plants outside of your water garden.

Take special consideration into the water sources before using it to grow and feed edible plants. It isn’t advisable to take water from your quarantine tank, possibly medicated with various chemicals, and use it to water your lettuce patch, to be consumed at a later date. Not only will this quarantine water contain herbal remedies and/or chemicals, but it harbors dangerous bacteria as well. While some bacteria from fish illnesses are harmless to humans, many are transferable and dangerous (not something to be consumed). Only consider using water from untreated tanks, with healthy fish and thriving plants, on plants intended for consumption. This is entirely possibly through appropriate stocking, use of sponge filters, sponges and ceramic media in hang on back filters, as well as various live aquatic plants, and aged water top offs.

Besides providing house plants, and garden patches, with a low dose of natural fertilizers, wastewater is generally free of contaminates. House plants are especially impacted by chlorine, water softeners, salts and fluorides, to name a few, causing wilting and browning, etc. Since many people readily utilize RO water, aged water and/or filtered water in their tanks, it’s safe to assume wastewater is free of many damaging characteristics. You will begin to see faster, more noticeable, growth in your garden, even with slower growing evergreens such as Creeping Juniper.

You can take it a step further, and use wastewater to produce a second commodity for something such as lasagna gardens. Composting is a very important and crucial aspect for most vegetable gardens, and even for flowers, by making use of kitchen waste – turning it into something helpful. When utilizing a compost pile, you must add moisture to help everything break down without overwatering (and leaving it in standing water). Not only does aquarium wastewater add fertilizers to a decomposing pile of kitchen cuttings, but it also introduces beneficial bacteria to further accelerate the composting process. This gives you yet another resource for gardening, or maybe even for maintaining houseplants, by simply keeping a fish tank.

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